The present invention relates to on-chip magnetic devices, and more specifically, to on-chip magnetic structures and methods for relieving stress and preventing wafer bowing.
On-chip magnetic inductors/transformers are important passive elements with applications in the fields such as on-chip power converters and radio frequency (RF) integrated circuits. In order to achieve high energy density, magnetic core materials with thickness ranging several 100 nm to a few microns are often implemented. For example, in order to achieve the high energy storage required for power management, on-chip inductors typically require relatively thick magnetic yoke materials (several microns or more). There are two basic configurations, closed yoke and solenoid structure inductors. The closed yoke has copper wire with magnetic material wrapped around it and the solenoid inductor has magnetic material with copper wire wrapped around it. Both inductor types benefit by having very thick magnetic materials. One issue with depositing thicker materials is tensile stress. Magnetic materials have tensile stress when deposited, wherein the stress in the thickness required for these materials can cause wafers to bow. The wafer bow can cause issues with lithography alignment and wafer chucking on processing tools, among others. Tensile stress for magnetic materials can be about 50 to about 400 megapascals (MPa). However, since the total magnetic film thickness requirement is greater than 1 micrometer (μm) to in excess of 1000 μm, wafer bow can be considerably high.